Serviceability, durability, and economical construction and operation are the main points to keep in mind when building greenhouses. No one denies that the full iron form of construction is the most durable and that it is also highly satisfactory when in operation, but the cost of construction is beyond the means of most vegetable growers. Again, it is doubtful whether full iron construction is the most economical in the end; the first cost is from one-third to one-half greater than for semi-iron construction, and this additional expense may exceed the cost of repairs in other types of construction. With proper care and painting the wood parts in a well-built house will last 25 years, and they could then be renewed at a cost which would not be burdensome to a grower who had harvested profitable crops for a quarter of a century. Iron pipe, concrete and thoroughly dried cypress are the most important materials needed in the construction of a modern commercial greenhouse.

176. Semi-Iron Type Of Construction

This is by far the most popular form of construction. The walls are usually concrete, and the 2-inch pipe posts which support the roof of tire house are often embedded in the concrete. If provision is made for walks or alleys along the walls in the greenhouse the posts should extend at least 6 feet 4 inches above the ground level. All purlins, braces and interior posts are made of iron pipes. The construction is of such a character that it is easily possible to replace decayed wood parts without disturbing the pipe posts, purlins or braces. Walks, beds and benches of concrete may be used if desired. Houses of this type are attractive, serviceable and durable. Any local carpenter can build them without difficulty, for nearly all wood parts are cut to the right dimensions at the factory and blue prints are furnished for the instruction of builders.